1. Field of the Invention
The present invention relates to a dynamoelectric machine such as an automotive alternator, etc., and a stator manufacturing method therefor, and particularly relates to a stator core construction and manufacturing method that improves circularity of an outer circumferential surface of a stator core that is fitted together with and supported by a case.
2. Description of the Related Art
A first conventional stator core that can be used in a dynamoelectric machine is prepared so as to have a cylindrical shape by curving and coiling up a band of steel plate in which a large number of slots and teeth have been formed along a first side and a large number of notches have been formed along a second side so as to be separated by a predetermined pitch from each other, and integrating it by welding (see a first patent document, for example). It has been claimed that superior roundness can be achieved in the stator core by forming the large number of notches along the second side of the band of steel plate so as to be separated by the predetermined pitch, and that circularity can be much improved particularly by forming the notches on surfaces behind the teeth.
A second conventional stator core is prepared so as to have a cylindrical shape by preparing a strip-shaped body bundle by laminating to a predetermined thickness strip-shaped bodies in which a large number of slots and teeth have been formed along a first side and integrating them by welding, bending the strip-shaped body bundle into a cylindrical shape, abutting end surfaces of the bent strip-shaped body bundle with each other, and integrating them by welding the abutted portions (see a second patent document, for example).
In the manufacturing method for this second conventional stator core, when the strip-shaped body bundle is bent into a cylindrical shape, bending in a vicinity of two end portions of the strip-shaped body bundle is less than in other portions, making abutted surfaces between the end surfaces of the bent strip-shaped body bundle misalign. If the abutted surfaces between the end surfaces of the bent strip-shaped body bundle are aligned forcibly and welded, roundness of the stator core deteriorates.
In order to solve the problems in the second conventional stator core that is described above, a third conventional stator core has been proposed in which the two end portions of the strip-shaped body bundle are bent so as to have a curvature that is approximately equal to a final curvature of the stator core before a step of bending the whole strip-shaped body bundle into a cylindrical shape (see a third patent document, for example). It has been claimed that because the two end portions of the strip-shaped body bundle are bent so as to have a curvature that is approximately equal to the final curvature of the stator core, the abutted surfaces between the end surfaces of the strip-shaped body bundle that has been bent into a cylindrical shape align when the strip-shaped body bundle is bent into a cylindrical shape, enabling roundness of the stator core to be improved.    First patent document: Japanese Patent Laid-Open No. HEI 10-225027 (Gazette)    Second patent document: Japanese Patent Laid-Open No. SHO 52-34301 (Gazette)    Third patent document: Japanese Patent Laid-Open No. 2001-298885 (Gazette)
In the first conventional stator core, because the large number of notches are formed along the second side of the band of steel plate, when the band of steel plate is curved and coiled up, notched portions become bend points, and an outer circumferential surface of the bent stator core becomes multangular. Consequently, it is necessary to adjust curving resistance (tensile resistance) of the band of steel plate while coiling it up so that the outer circumferential surface shape does not become multangular, making the manufacturing process for the stator core complicated. Because the band of steel plate that has been coiled up into a cylindrical shape is integrated by welding it at the notched portions, even if the band of steel plate has been coiled up so as to have good roundness, the band of steel plate may deform locally due to heat during welding, reducing its roundness.
In the third conventional stator core, the two end portions of the strip-shaped body bundle are bent so as to have a predetermined curvature before the step of bending the whole strip-shaped body into a cylindrical shape, but satisfactory roundness has not been achieved.
In addition, in the first through third conventional stator cores, tension continues to act on the steel plates that constitute the stator cores after they have been prepared. When a dynamoelectric machine that incorporates such a stator core is mounted to a vehicle, the stator core is subjected to vehicle vibration, and there has therefore been a danger that cracking or other damage may arise at positions on the steel plates where such tension is acting.